ANGUISH:Even though she has joint custody, Kelly Rutherford can only be with kids Hermes, 5, and Helena, 3, in France, where her ex, Daniel Giersch (below), keeps them by court decree.

(EPA)

(
)

They fall hard for charming Europeans and only later realize they’ve married someone they barely know who has whisked their children away.

Stars, they’re just like us.

It’s two days after the start of the school year at the private academies of the Upper East Side, but instead of picking up her two kids, “Gossip Girl” star Kelly Rutherford, 43, is nervously pacing outside her empty Madison Avenue apartment, walking her dog.

When she starts shooting her final season as Lily Van Der Woodsen this week, her children, Hermes, 5, and Helena, 3, will start classes in France and via Skype tell their mom about their day.

“My little girl’s a baby,” Rutherford told The Post. A rep for Rutherford declined an interview, but the actress spoke to The Post outside her building.

“She’s never been away from me in her life and all of a sudden I’ve been reduced to a visitor. It doesn’t make sense.”

For the past three decades, Rutherford has been acting out soap operas — first on “Melrose Place” as an ex-hooker hired to seduce a man she falls in love with, and for the past five years as the billionaire socialite mom on “Gossip Girl.”

But none of her melodramatic story lines, she said, properly prepared her for the bruising, real-life custody battle with her ex-husband, Daniel Giersch.

“I’m living a mother’s worst nightmare,” she said.

Rutherford asked Los Angeles County Superior Court Judge Teresa Beaudet for a stay to allow her children to return from visiting their father in France in time for school on Sept. 2. The judge ruled the children must stay in France as long as their father’s visa is revoked.

“I didn’t think they would never come back,” Rutherford said.

Rutherford met Giersch, a German businessman six years her junior, in Beverly Hills in 2006 when a waitress friend at Il Fornaio set them up. The blond actress had been married once before — an ill-fated seven-month union with Venezuelan banker Carlos Tarajano, which ended in divorce in 2002.

“I was really in love in the beginning,” she admitted.

Friends said Rutherford was too trusting of her new partner from the get-go.

“He looks right through you in a scary way,” said a close friend of Rutherford’s. “He charmed Kelly, and she fell in love with him, and he turned out to be somebody completely different during the marriage. Americans can be a little naïve about these charming Europeans.”

Rutherford said the primary reason she eventually left “was because there were other women. I found him e-mailing one night, saying he was sorry he couldn’t meet up. I was only married to him for just over two years. You don’t see it coming, you think something’s wrong with you.”

The couple split in 2009, when Rutherford was pregnant with their daughter, using a large handbag as a prop on the show to cover her baby bump. Now the Upper East Side mom is living in a prematurely empty nest.

‘He hasn’t had to show any documentation of why his visa was revoked, or if he’s even tried to overturn that as he’s supposed to do to come back to the US,” Rutherford said. “Meanwhile, I’ve had to show my work schedule and all of my finances.”

Since the father can’t come to the United States until he gets a new visa, Beaudet ruled that the kids would stay in France with Giersch and Rutherford would travel to see them.

Under Beaudet’s ruling, Giersch has to buy Rutherford six commercial plane tickets a year to visit her kids in France, and provide her a home and a car while she’s abroad. Rutherford still has joint custody of her kids.

The businessman made his money suing Google for the rights to the name “Gmail,” since he trademarked “G-mail” for a German mail service he started in 2000.

“Why France? Nobody lives in France,” fumed Rutherford. “He doesn’t live in France. His mother’s boyfriend has a house there. That’s it. He lives in Monaco. The whole thing is the most bizarre thing. I keep thinking, how is this possible?”

Rutherford said she’s looking forward to the distraction of work. The show starts shooting here this week.

“The cast members were close with the kids. They were always offering to baby-sit,” she said, referring to the young cast, including A-listers like Blake Lively and Leighton Meester.

“I would joke, ‘Sure, when you’re done with your Vogue cover shoot, you can come over and baby-sit my kids.’ ”